[TowerTalk] [Bulk] Re: Rotator Choice for Larger Yagi

Wed May 4 13:25:50 EDT 2016

Grant,

 From what I read their main function is to dampen the torsional shock 
loads.
Here is what Mercedes Benz says:
"The flexible discs serve two functions on the vehicle.  Primarily to 
absorb excessive torsional shock applied to the drive shaft under hard 
acceleration and deceleration.  They also isolate the drive shaft from 
vibration while still transferring power from the transmission to the 
differential. "

Jon,  W4ABC brought up an interesting consideration.  Unless they are 
isolated from the
axial load involving the mast and antennas the disc will be supporting 
the load.  Will they do their
dampening job when they are supporting a load ?  Doesn't sound like they 
would.
In my case I will be supporting 99% of the load from the thrust bearing 
above.  So probably not a concern.

Lastly found this interesting post from the Tower Talk archives. Seems 
the bolts coming loose is a
common issue.

73,
Bob

Hi Jim,

Warren, KE6LEA and I built one these flex-disc shock mount for one of the towers
at the Caltech Amateur Radio Club. We used a Mercedes-Benz Flex Disc (a.k.a.
Hardy Disc) coupled on one end to the output spindle of an M-Squared Orion
OR-2800 rotator, and a homebrew steel mast clamp flange on the other. The system
is used to turn a KLM 4el 40M yagi and KT-34XA both with the heavy duty
boom options (~ 300 lbs of antenna). Our first inspection of the installation
earlier in the summer revealed that several of the grade 8 flange bolts had fallen
out of the steel flange, so we added a set of grade 8 jam nuts to each of the
6 flange bolts. After getting a considerable workout in Sweepstakes and CQ WW,
I need to go back up the tower sometime soon and inspect all the hardware
to see if anything has loosened.

You can see pictures of the setup athttp://www.its.caltech.edu/~w6ue/antenna-pictures.html 
<http://www.its.caltech.edu/%7Ew6ue/antenna-pictures.html>

73 de Mike, W4EF.............

Bob
K6UJ

On 5/4/16 9:31 AM, Grant Saviers wrote:
> Ok, it's what we call in the US a "Lovejoy" coupling.  I don't see how 
> it can handle axial loads.   The installation instructions specify the 
> distance between the end plates of the two shafts.
>
> The specs do show a maximum vibration torque level much less than the 
> static value.   "Alternating Torque TKW"
>
> The mast above the coupling in the jpg must be held axially by 
> bearings somewhere.
>
> Again, these are engineered for vibration and shaft alignment 
> management and are much less effective for shock damping.
>
> some specs at 
> http://onlinetools.ktr.com/cgi-bin/webkup.exe?Mod=2&La=en&P=02&B=001&Z=45
> installation at 
> https://www.ktr.com/fileadmin/ktr/media/Manuals/40210en000000.pdf
>
> Grant KZ1W
>
> On 5/4/2016 8:44 AM, Máximo EA1DDO_HK1H wrote:
>> Grant, please, check the "*Flex Shock Mount Clamp*";
>>
>> http://www.ure.es/media/kunena/attachments/1956/3akp1012800x600.jpg
>>
>> Available in many different sizes, power and even colours (aka quality);
>>
>> https://www.ktr.com/en/products/power-transmission-technology/couplings/flexible-jaw-and-pin-bush-couplings/rotex/rotex-standard/
>>
>> 73, Maximo
>>
>> > To: jonpearl at tampabay.rr.com; k6uj at pacbell.net; 
>> towertalk at contesting.com
>> > From: grants2 at pacbell.net
>> > Date: Wed, 4 May 2016 08:39:02 -0700
>> > Subject: Re: [TowerTalk] [Bulk] Re: Rotator Choice for Larger Yagi
>> >
>> > You ask a very important question. Can these handle the static axial
>> > load of mast and antennas?
>> >
>> > http://www.wholesaleimportparts.com/driveshaft.php for a picture of 
>> one
>> > with mating assemblies.
>> >
>> > A complexity is how the shaft (mast) is supported either side of the
>> > coupling as I don't think they are designed to handle large sideways
>> > torques or axial thrust - i.e. each shaft is held in alignment by two
>> > bearings which also control the axial dimension, which would not be 
>> the
>> > case in using one above a rotator and something else at the tower top.
>> > If the something else was a tube sleeve then it constrains the 
>> angle the
>> > mast can attain, but not the axial dimension. If the something else is
>> > the typical "thrust bearing" then the shaft can move to some 
>> surprising
>> > angles, but does have axial constraint. In neither case would a HyGain
>> > or Yaesu design rotator really be two bearings holding its output
>> > "shaft", except when the dead (axial) load is sufficient to keep the
>> > races tight under all circumstances. Other rotator designs have
>> > constrained shafts with two or more bearings.
>> >
>> > The common "Lovejoy" coupling is another version of a rubber isolated
>> > coupling in common use in many sizes. Again, it is used where both
>> > shafts are rigidly constrained radially and axially. A Lovejoy is
>> > specified to handle x degrees of misalignment and y thousands of an 
>> inch
>> > of shaft offset, at an rpm and torque value. I think those are the
>> > primary objectives, not shock absorption. A Lovejoy is not intended to
>> > take axial loads, so would be a bad choice without shaft constraints.
>> >
>> > The picture of the driveshaft components also leads me to suspect that
>> > pins, not bolts are the shaft to coupling connection, so the intent is
>> > no axial load on the rubber coupling.
>> >
>> > The link recently posted
>> > http://m4.i.pbase.com/v3/91/283791/1/50045854.P0001095.JPG shows a
>> > rubber coupler design with what appears to have solutions to the 
>> issues
>> > above. The tube above the rotator clearly doesn't turn and it appears
>> > to have a bearing at the end for the mast inside. Looking closely, it
>> > appears the end of the mast has a spline that mates with the top
>> > attachment to the coupling. Thus, no thrust load can be placed on the
>> > coupling.
>> >
>> > A tower with antennas is a very complex dynamic system - many 
>> masses and
>> > springs and few energy absorption elements. My reasoning is the shock
>> > and vibration loads cause the destruction from high amplitude
>> > oscillations or when hard stops are hit - rotator brakes and gears all
>> > have backlash. Loose mast and boom clamps and rotator bolts are 
>> another
>> > source. Peened out shear pin holes are a sure sign of problems.
>> > Another concern with a rubber isolator is it adds another spring (with
>> > low damping) into a system that has unknown dynamic properties. It is
>> > an offset to the benefit of the rubber isolator ability to reduce the
>> > peak torque values by spreading a shock pulse energy out over time.
>> > Another potentially large force can be created by adding a "balancing
>> > weight" at the end of a boom, so the boom is statically balanced at 
>> the
>> > mast attachment. However, that adds a weight on the end of a 
>> cantilever
>> > beam spring, when the other element masses are distributed along it.
>> > I've seen it done to ease of tramming the antenna, but adding to the
>> > rotational inertia is not good.
>> >
>> > One also might question what these couplings are really designed to 
>> do.
>> > Shock transients are large amplitude low frequency content events.
>> > Vibrations are small amplitude higher frequency and usually 
>> continuous.
>> > Rubber isolators generally don't have much damping at low frequencies,
>> > which are what I see when my aluminum starts waving around in a storm.
>> >
>> > Another idea is to adapt a rubber spring torsion axle as an isolator.
>> > These are used on smaller trailers and can handle loads in multiple
>> > axis. Again, with very limited damping loss.
>> >
>> > http://www.northerntool.com/shop/tools/product_200649004_200649004
>> >
>> > Grant KZ1W
>> >
>> >
>> >
>> > On 5/3/2016 23:01 PM, Jon Pearl - W4ABC wrote:
>> > > Hi Bob and Jim,
>> > >
>> > >
>> > > There's a whole bunch of videos on Youtube on their typical use, but
>> > > these two get to the point pretty quickly with some good close-ups:
>> > > https://www.youtube.com/watch?v=4yCxhyTlysw &
>> > > https://www.youtube.com/watch?v=v71KGSCjBrQ
>> > >
>> > > Bob - as to your prior question in the earlier email, I would 
>> imagine
>> > > any decent driveshaft shop could come up with 3 bolt flanges to weld
>> > > onto whatever you could drag into their shop and do so
>> > > concentrically. In searching, I see that there are also 4 bolt 
>> models
>> > > of flanges and flex joints. I would think that the 6 bolt versions
>> > > would provide more cushion for rotator purposes as there is more
>> > > rubber between the bolts.
>> > >
>> > >
>> > > I have a question about the use of one of these devices, though.
>> > >
>> > > Would it be possible or more likely *wise* to allow the weight of a
>> > > mast and antennas to come to rest directly on the flex joint,
>> > > compressing it (distorting it) between its two flanges? Its primary
>> > > function in automotive use is to reduce vibration through the
>> > > regularly anticipated twist of a drive shaft, not to be heavily
>> > > compressed between the transmission and pumpkin. I wouldn't mind
>> > > trying one of these flex joints, but I would hate to have to use a
>> > > bearing shelf, collar and bearing to hold the weight of the mast and
>> > > antennas off of the joint.
>> > >
> snip... 